Re: [PATCH v3 12/13] mm/huge_memory: add and use normal_or_softleaf_folio_pmd()

Suren Baghdasaryan
2026-03-28T19:45:24Z

On Fri, Mar 20, 2026 at 11:08 AM Lorenzo Stoakes (Oracle)
<ljs@kernel.org> wrote:
>
> Now we have pmd_to_softleaf_folio() available to us which also raises a
> CONFIG_DEBUG_VM warning if unexpectedly an invalid softleaf entry, we can
> now abstract folio handling altogether.
>
> vm_normal_folio() deals with the huge zero page (which is present), as well
> as PFN map/mixed map mappings in both cases returning NULL.
>
> Otherwise, we try to obtain the softleaf folio.
>
> This makes the logic far easier to comprehend and has it use the standard
> vm_normal_folio_pmd() path for decoding of present entries.
>
> Finally, we have to update the flushing logic to only do so if a folio is
> established.
>
> This patch also makes the 'is_present' value more accurate - because PFN
> map, mixed map and zero huge pages are present, just not present and
> 'normal'.
>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

One clarifying question below but I think I know the answer, just want
to double-check.

> ---
> mm/huge_memory.c | 47 +++++++++++++++++++----------------------------
> 1 file changed, 19 insertions(+), 28 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9ddf38d68406..5831966391bd 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2342,10 +2342,6 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
> add_mm_counter(mm, mm_counter_file(folio),
> -HPAGE_PMD_NR);
>
> - /*
> - * Use flush_needed to indicate whether the PMD entry
> - * is present, instead of checking pmd_present() again.
> - */
> if (is_present && pmd_young(pmdval) &&
> likely(vma_has_recency(vma)))
> folio_mark_accessed(folio);
> @@ -2356,6 +2352,17 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
> folio_put(folio);
> }
>
> +static struct folio *normal_or_softleaf_folio_pmd(struct vm_area_struct *vma,
> + unsigned long addr, pmd_t pmdval, bool is_present)
> +{
> + if (is_present)
> + return vm_normal_folio_pmd(vma, addr, pmdval);
> +
> + if (!thp_migration_supported())
> + WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> + return pmd_to_softleaf_folio(pmdval);
> +}
> +
> /**
> * zap_huge_pmd - Zap a huge THP which is of PMD size.
> * @tlb: The MMU gather TLB state associated with the operation.
> @@ -2390,36 +2397,20 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> tlb->fullmm);
> arch_check_zapped_pmd(vma, orig_pmd);
> tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
> - if (vma_is_special_huge(vma))
> - goto out;
> - if (is_huge_zero_pmd(orig_pmd)) {
> - if (!vma_is_dax(vma))
> - has_deposit = true;
> - goto out;
> - }
>
> - if (pmd_present(orig_pmd)) {
> - folio = pmd_folio(orig_pmd);
> - is_present = true;
> - } else if (pmd_is_valid_softleaf(orig_pmd)) {
> - const softleaf_t entry = softleaf_from_pmd(orig_pmd);
> + is_present = pmd_present(orig_pmd);

nit: With this you don't need to initialize is_present anymore when
you define it.

> + folio = normal_or_softleaf_folio_pmd(vma, addr, orig_pmd, is_present);
> + if (folio)
> + zap_huge_pmd_folio(mm, vma, orig_pmd, folio, is_present,
> + &has_deposit);
> + else if (is_huge_zero_pmd(orig_pmd))
> + has_deposit = !vma_is_dax(vma);
>
> - folio = softleaf_to_folio(entry);
> - if (!thp_migration_supported())
> - WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> - } else {
> - WARN_ON_ONCE(true);
> - goto out;
> - }
> -
> - zap_huge_pmd_folio(mm, vma, orig_pmd, folio, is_present, &has_deposit);
> -
> -out:
> if (has_deposit)
> zap_deposited_table(mm, pmd);
>
> spin_unlock(ptl);
> - if (is_present)
> + if (is_present && folio)

In which case would you have a valid folio and !is_present? Is that
the softleaf case?

> tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
> return true;
> }
> --
> 2.53.0
>